The present invention relates to a process for thermal development and transfer. More particularly, it is concerned with an improvement in a process for forming color pictures employing a photosensitive material containing a pigment donating substance which releases a mobile hydrophilic pigment upon thermal development, and an image receiving material having a pigment fixing layer.
There is known a photosensitive material composed of a support on which is deposited at least a photosensitive silver halide, an organic silver salt as an oxidizing agent, a binder and a pigment donating substance having a reducing effect on the silver halide and/or the organic silver salt and reacting with the silver halide and/or the organic silver salt under heat to release a hydrophilic pigment. Such a photosensitive material is disclosed in Japanese Patent Application No. 157798/1981. This material has the advantage that the thermal development of an image after exposure is sufficient to form simultaneously a silver-based image in an exposed area and a mobile hydrophilic pigment in an area corresponding to the silver-based image. More specifically, if an image formed by exposure is subjected to thermal development, an oxidation-reduction reaction takes place between the organic silver salt and the reducing pigment donating substance to form a silver-based image in the exposed area, while the exposed photosensitive silver halide acts as a catalyst for the reaction. The pigment donating substance is oxidized by the organic silver salt to form an oxide. This oxide is decomposed in the presence of a pigment releasing assistant and releases a mobile hydrophilic pigment. The silver image and the mobile hydrophilic pigment are thus obtained in the exposed area, and a color picture is obtained when the pigment is transferred onto an image receiving material. If an autopositive emulsion is employed for the photosensitive layer, the silver image and the mobile hydrophilic pigment are formed in the unexposed area.
Another photosensitive material is disclosed in Japanese Patent Application No. 26008/1983 filed by the assigneee of this invention on Feb. 18, 1983 and entitled "Image Forming Process". In that material, on a support is deposited at least a photosensitive silver halide, a binder and a photosensitive layer containing an immobile pigment donating substance which is reducing and releases a mobile hydrophilic pigment under heat but ceases to release the pigment upon reaction with the silver halide. This material enables, only if subjected to thermal development after exposure, the simultaneous formation of a silver-based image in the exposed area and a mobile hydrophilic pigment in areas other than the silver-based image.
The immobile pigment donating substance ceases to release the hydrophilic pigment if it is oxidized. If the photsensitive material is heated after exposure, an oxidation-reduction reaction takes place between the organic silver salt and/or photosensitive silver halide and the pigment donating substance to form a silver-based image in the exposed area, while the exposed silver halide acts as a catalyst for the reaction. The pigment donating substance forms an oxide and ceases to release the hydrophilic pigment in the exposed area, and the mobile hydrophilic pigment is therefore obtained only in the unexposed area. If an autopositive emulsion is employed for the photosensitive layer, the silver-based image is formed in the unexposed area and the mobile hydrophilic pigment in the exposed area.
The image receiving material has an image receiving layer formed on a support for receiving the pigment released from the photosensitive material by thermal development as hereinabove described. The image receiving layer contains a pigment fixing agent, such as a pigment mordant. The pigment fixing agent is selected so as to suit the physical properties of the pigment, the other constituents of the photosensitive material and the conditions of transfer. It is possible to use, for example, a high polymer mordant as disclosed in Japanese Patent Application No. 157798/1981.
It is necessary to supply a diffusion assistant to the image receiving material before placing it on the photosensitive material for transfer purposes. If the diffusion assistant is of the type which is converted to a liquid when heated, such as urea, water of crystallization or an agent in a microcapsule, it is incorporated into the image receiving material during its production, and need not be supplied before it is placed on the photosensitive material. If, on the other hand, the diffusion assistant is water or an aqueous solution, it must be supplied to the image receiving material when it is placed on the photosensitive material.